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Diffstat (limited to 'doc')
| -rw-r--r-- | doc/src/examples/collidingmice-example.qdoc | 39 |
1 files changed, 21 insertions, 18 deletions
diff --git a/doc/src/examples/collidingmice-example.qdoc b/doc/src/examples/collidingmice-example.qdoc index 7ea2ca2..657a204 100644 --- a/doc/src/examples/collidingmice-example.qdoc +++ b/doc/src/examples/collidingmice-example.qdoc @@ -66,7 +66,7 @@ \section1 Mouse Class Definition - The \c mouse class inherits both QObject and QGraphicsItem. The + The \c mouse class inherits from QGraphicsItem. The QGraphicsItem class is the base class for all graphical items in the Graphics View framework, and provides a light-weight foundation for writing your own custom items. @@ -78,14 +78,11 @@ {QGraphicsItem::}{boundingRect()}, which returns an estimate of the area painted by the item, and \l {QGraphicsItem::}{paint()}, which implements the actual painting. In addition, we reimplement - the \l {QGraphicsItem::}{shape()} function to return an accurate + the \l {QGraphicsItem::}{shape()} and \l {QGraphicsItem::}{advance()}. + We reimplement \l {QGraphicsItem::}{shape()} to return an accurate shape of our mouse item; the default implementation simply returns - the item's bounding rectangle. - - The rationale for deriving from QObject in addition to - QGraphicsItem is to be able to animate our items by reimplementing - QObject's \l {QObject::}{timerEvent()} function and use - QObject::startTimer() to generate timer events. + the item's bounding rectangle. We reimplement \l {QGraphicsItem::}{advance()} + to handle the animation so it all happens on one update. \section1 Mouse Class Definition @@ -105,19 +102,18 @@ calling the item's \l {QGraphicsItem::rotate()}{rotate()} function we alter the direction in which the mouse will start moving. - In the end we call QObject's \l {QObject::}{startTimer()} - function, emitting a timer event every 1000/33 millisecond. This - enables us to animate our mouse item using our reimplementation of - the \l {QObject::}{timerEvent()} function; whenever a mouse - receives a timer event it will trigger \l - {QObject::}{timerEvent()}: - + When the QGraphicsScene decides to advance the scene a frame it will call + QGraphicsItem::advance() on each of the items. This enables us to animate + our mouse using our reimplementation of the advance() function. + \snippet examples/graphicsview/collidingmice/mouse.cpp 4 \snippet examples/graphicsview/collidingmice/mouse.cpp 5 \snippet examples/graphicsview/collidingmice/mouse.cpp 6 - First we ensure that the mice stays within a circle with a radius - of 150 pixels. + First, we don't bother doing any advance if the step is 0 since we want to our advance in + the actual advance (advance() is called twice, once with step == 0 indicating that items + are about to advance and with step == 1 for the actual advance). We also ensure that the + mice stays within a circle with a radius of 150 pixels. Note the \l {QGraphicsItem::mapFromScene()}{mapFromScene()} function provided by QGraphicsItem. This function maps a position @@ -275,5 +271,12 @@ In the end, we set the application window's title and size before we enter the main event loop using the QApplication::exec() function. -*/ + Finally, we create a QTimer and connect its timeout() signal to the advance() + slot of the scene. Every time the timer fires, the scene will advance one frame. + We then tell the timer to fire every 1000/33 millisecond. This will + give us a frame rate of 30 frames a second, which is fast enough for most animations. + Doing the animation with a single timer connect to advance the scene ensures that all the + mice are moved at one point and, more importantly, only one update is sent to the screen + after all the mice have moved. +*/
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